COPY problem

I am trying to populate a table using the COPY command, but the command
keeps failing with a 'Query was cancelled error'. When I re-run the
exact same command, it usually fails at a different spot, and
occasionally succeeds. Here's an example:

analytics=# COPY tbl555 FROM '/usr/local/pgsql/xaa' WITH NULL AS '';
ERROR:  copy: line 167641, Query was cancelled.
analytics=# COPY tbl555 FROM '/usr/local/pgsql/xaa' WITH NULL AS '';
ERROR:  copy: line 164863, Query was cancelled.
analytics=# COPY tbl555 FROM '/usr/local/pgsql/xaa' WITH NULL AS '';
ERROR:  copy: line 117599, Query was cancelled.

It is a brand new 7.3.3 database on Debian 3.0 on skookum(tm) hardware
(p4, 1G ram). Currently there is only one user on the system (me), and
other apps running are sshd, tomcat, etc, but they're not being used.

I have a text file with approx 20 million records, split into 20 files
of 1 million records each. I also previously tried with smaller files
(100,000 records each) with about a 50% probability of the COPY command
succeeding.

The table itself has 9 columns (3 text, 4 numeric, 1 date) and the data
in the file is tab delimited. Whenever a problem occurs and I reference
the line in the file, there is no apparent error, and when I re-run the
COPY it usually succeeds.

Anyone have any ideas on how I can solve this?

TIA

Ron